1. Field of the Invention
This invention pertains to articulated vehicles, such as rough terrain vehicles especially suitable for logging operations and the like. More particularly, this invention pertains to a cradle mounting assembly for the front axle of a rough terrain vehicle.
2. Description of the Prior Art
In a rough terrain vehicle of the prior art the cradle mounting assembly comprised bearing blocks carried on the frame to receive the bushings. In many cases, these blocks were line-bored to assure that the bearings supporting the cradle assembly would be axially aligned when the cradle assembly mounted in place on the frame. Although a spherical bushing having metal-to-metal contact could be used in a cradle assembly having the bearing blocks individually bored and welded in place without exceeding the allowable machining tolerances for the mounting assembly, such bushings are particularly vulnerable to environmental excess in a rough terrain vehicle used in forestry operations. Metal-on-metal bushings for rough terrain vehicles require an extremely tight manufacturing tolerance to keep the joint clean, as well as constant greasing in an effort to preserve the life of the seals and the bushing. The constant exposure of the joint to mud and grime permits grit to work into the joint and act as a grinding compound thereon. Further, the steel-to-steel contact in the old design tended to pound out the bore of the cradle assembly during operation. Also, the metal-on-metal contact provided by the prior art bushing transmitted all wheel and axle shock loads directly to the main chassis.
The cradle mounting assembly of the present invention eliminates the need for line boring of cradle mounting blocks required in the prior assembly. Coupling means provided between the cradle and a spherical bearing carried in each of the mounting blocks assures alignment of the cradle assembly without expensive line-boring procedures.
Further, the elastomeric bearing provided between the inner and outer races of the bushing protects the joint from the environmental effects of dirt and grime encountered under normal operation conditions.
Further, the mounting block assembly of the present invention enables the bushing to be readily removed from the frame, permitting simple replacement of the cradle assembly.
Under load, the elastomeric interface of the spherical bushing of the present invention provides a progressively higher resistance moment as cradle movement is increased relative to the front frame. The capability of the bushing to dampen such forces exerted under combined loading theoretically eliminates the need for axial thrust washers between the cradle and the front frame and the need for frame stops to stop oscillatory movement of the cradle relative to the front frame. In practice, impact forces between the cradle and the stops are lessened. Further, the intent of the improved design is to assure that each bearing shares the input loads equally to stabilize the vehicle about its longitudinal axis.
Although spherical rubber bushings have been employed in other applications, such bushings have not been used in combination with the connecting means of a cradle mounting assembly. Further, such applications neither solve nor make obvious the solution provided by the present invention. For example, in U.S. Pat. No. 2,305,880 -- Leighton, issued Dec. 22, 1942 and entitled "Oscillatory Connection", the spherical rubber bushing is employed in a steering linkage requiring oscillatory parts. However, such linkage offers no solution to the combined alignment and oscillatory problem found in the present cradle mounting assembly. In U.S. Pat. No. 2,996,308 -- Cislo, issued Aug. 15, 1961 and entitled "Self-Aligning Suspension Control Arm Bearing Assembly", a pivot shaft threaded at opposite ends is received in respective spherical bushings. Although the Cislo patent also shows a spherical bushing, it, too, fails to solve the combined oscillation and alignment problem of the prior design and such assembly does not teach or suggest the cradle mounting assembly of the present invention.
Further, neither of the above-noted patents suggest a mounting assembly suitable for a power-driven axle.